They quit putting the 205s in Blazers long before yours. They'll have a three bolt cover right smack in the middle of the back side of the housing. Unlike the 203s and 208s, the 205 is a gear driven transfer case and the cover is for the idler gear shaft. The 203s have a 2.01:1 low range, the 205s have a 1.96:1 low range and the 208s have a 2.61:1 low range.
What year did you say your Blazer was again? All three were found under Blazers at one time or another.